Halos & Sundogs

Ice crystal prisms

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Hexagonal ice crystals act as 60° prisms.
• Minimum deviation of about 22° creates the 22° halo.
• Horizontally aligned plates make sundogs beside the Sun.

Steps

1. Six-sided prisms
2. Minimum deviation
3. The 46° halo
4. Sundogs
5. Piling up at 22°
6. Halo in Moon widths